1. Field of the Invention
The present invention is directed to an electrode, a method of producing the same and a solid-state high molecular weight electrolyte type fuel cell employing the electrode.
2. Description of the Related Art
Referring to FIG. 5, there is illustrated a cross-section of a conventional or well-known fuel cell of the solid-state high molecular weight electrolyte membrane type. In such a fuel cell, a solid-state high molecular weight electrolyte membrane 20 is sandwiched or interposed between a pair of fuel cell electrodes, fuel electrode 21 and oxygen electrode 22, to constitute a membrane electrode assembly 30 which will be hereinafter abbreviated to “MEA.” The MEA 30 is held between a pair of separators (neither is shown). At an interface between each of the separators and its corresponding electrode, the fuel electrode and the oxygen electrode are formed with a fuel gas passage and an oxidizing gas passage, respectively.
The fuel electrode 21 and the oxygen electrode 22 are produced by providing catalyst layers 21b and 22b on surfaces of electrode structures 21a and 22a, respectively. The pair of fuel electrode 21 and oxygen electrode 22 hold or sandwich therebetween the membrane 20 so as to establish close or intimate contact of the respective catalyst layers 21b and 22b with the membrane 20. Each of the electrode structures 21a and 22a is electrically conductive and gas permeable. Each of the electrode structures 21a and 22a acts as both a gas dispersion layer and a current collector. One of the gas dispersion layers is for flowing the gas from one of the electrodes to the catalyst layer 21b, while the other of the gas dispersion layers is for flowing the gas from the other of the electrodes to the catalyst layer 22b. The current collector passes electrons therethrough.
The gas supplied to the fuel electrode 21 moves to the catalyst layer 21b through the electrode structure 21a to produce the following reaction.2H2→4H++4e−
The resultant hydrogen ions (4H+) pass through the membrane 20 to reach the oxygen electrode 22. Concurrently, the electrons (4e−) produced at the catalyst layer 21b by the foregoing reaction arrive at the catalyst layer 22b of the oxygen electrode 22 by way of the catalyst layer 21b, the electrode structure 21 a and an external circuit 40 including an external load 41.
On the other hand, at the oxygen electrode 22, the oxidizing gas reaches the catalyst layer 22b after passing through the electrode structure 22. The oxygen in the oxidizing gas is deoxidized by coupling with the electrons (4e−) and is coupled with hydrogen ions (4H+) which come from the fuel electrode 21 through the membrane 20, as apparent from the following reaction.O2+4H++4e−→2H2O
Some of the resultant water enters the membrane 20, due to the concentration gradient, to move toward the fuel electrode 21 in a dispersed fashion, while the remaining water is changed into its gas phase or vapor, to be discharged together with an off-gas of the oxidizing gas after being dispersed to the gas passage by way of the catalyst layer 22b and the electrode structure 22a. Thus, the fuel cell functions as a battery since it produces electrons to generate an electric current.
As described above in great detail, the conventional fuel cell is constructed such that the catalyst layer is provided on each surface of the electrode structure, which acts as both the gas dispersion layer and the current collector.
However, the conventional fuel cell has problems or drawbacks in that the catalyst utilization rate is low, the internal resistance is large, and the gas and produced water dispersions are subject to be in a velocity controlling step. Thus, the output characteristic of the conventional fuel cell remains insufficient.